My last 406 had World products Sportsman II heads,Comp cams X-treme hydraulic cam,.507 int..510 ex. With flattop pistons and a 650 dbl.pumper.It went 13.15 in the quarter on motor,the way I drove it everyday.12.49 at 113mph. on a 150 shot of NOS. At 3950lbs. with 275/60-15 radials.Not bad.If you got a few bucks,get the aftermarket heads,but fuelie heads with some pocket porting work pretty well also.
